1. Field of the Invention
The present invention relates to a magnetic recording medium for use in hard disk drives or the like. And more particularly, it relates a magnetic recording disk having a fine surface, irregularity structure (texture) on its surface and a method of manufacturing such a magnetic recording disk.
2. Description of the Related Art
Magnetic recording disks for use in conventional hard disk drives or the like comprise an Nixe2x80x94P layer, a magnetic layer, a protective film, a surface lubricating layer, etc. successively formed on a surface of a substrate made of an aluminum material or the like. In recent years, a glass substrate has been finding practical use in place of the aluminum substrate to meet demands for hardness and smoothness.
The above hard disk drives have heads with a minimized lift, i.e., a semicontact head, in view of ever-increasing demands for higher recording density. Therefore, it has been desired to make the surface of magnetic recording disks smoother. However, if the surface of magnetic recording disks is too smooth, it attracts the head to the extent the head sticks inseparably to the surface. As a result, the surface of magnetic recording disks should preferably have certain microscopic surface irregularities (texture).
The texture of conventional magnetic recording disks has been formed by a mechanical abrading process to abrade the surface of the Nixe2x80x94P layer or the like on the aluminum substrate with an abrasive tape or an abrasive cloth.
If an abrasive tape is used, then the abrasive tape carries abrasive grain bonded to its opposite surfaces to abrade the surface of the disk. Specifically, the abrasive tape is pressed against the surface of the disk, and the surface of the disk is rotated to produce abrasive grooves thereon for thereby forming a texture structure composed of fine surface irregularities. If an abrasive cloth is used, then an abrasive solution containing abrasive grain is dropped onto the abrasive cloth, and the surface of the disk to be abraded is pressed against the abrasive cloth and rotated to produce abrasive grooves thereon.
Fine surface irregularities (texture) are formed on the surface of a magnetic recording disk having a glass substrate by dissolving the surface with a vapor of hydrofluoric acid or crystalline deposition. When a texture is formed on the surface of a magnetic recording disk by dissolving the surface with a vapor of hydrofluoric acid, the surface is dissolved at locally different rates due to different vapor adsorption or density rates to form fine surface irregularities on the surface. When crystalline deposition method is employed, the size of crystal grain in the glass substrate is controlled by heat treatment to separate crystal grain irregularities on the surface, turning the surface into a fine surface irregularity structure.
In the mechanical texture forming processes using the abrasive tape or the abrasive cloth, the accuracy is poor, and the surface irregularities suffer large variations. These problems make it difficult to use a semicontact head whose lift is about 30 nm.
It has been attempted to apply a laser beam to form the fine surface irregularity structure (texture). Specifically, a laser beam having a very small diameter focused by a lens and a focusing mirror is scanned over and applied to the surface of the disk to concentrate the energy of the laser beam on a small area. The concentrated laser beam brings about a laser abrasion phenomenon to produce crater-like surface irregularities at regular intervals as the texture structure.
Usually, a pulse laser is used to produce the above laser abrasion phenomenon. Height variations of the surface irregularities may possibly be caused by variations of laser spot diameter and laser beam intensity depending on the position on the disk, and time-dependent variations of laser intensity. A limitation on the number that the laser beam can repeatedly be applied (the frequency at which the laser beam is applied) is considered to result in a limitation on the number of surface irregularities. Therefore, it needs a long process time to form a texture structure on the entire disk surface with a laser beam. When a surface irregularity structure having a height of 20 nm or less is needed as a fine texture for a high magnetic recording density, the frequency at which the pulsed laser beam is to be repeatedly applied usually ranges from 1 to 10 kHz. Consequently, if surface irregularities are to be formed in the shape of regular triangles at a pitch of 10 xcexcm, then about 115 tens of thousands of surface irregularities have to be produced per 1 cm2. It takes about 1156 second/cm2 if the repetition frequency is 1 kHz, and 115 second/cm2 if the repetition frequency is 10 kHz. Thus, it requires a long process time to form a texture structure on the entire disk surface, resulting in problems of high cost and process time, which make the process not practical.
When a metal surface is left to stand in the atmosphere, a natural oxide layer is usually formed on the outermost surface layer. Though the natural oxide layer takes a different form depending on the material thereof, a natural oxide layer having a thickness of 3-5 nm is formed on an Nixe2x80x94P layer on an aluminum material. In the process based on the laser abrasion phenomenon, the natural oxide layer and a non-oxide layer have different characteristics to absorb and reflect the laser beam. Therefore, when the disk surface is melted by the laser abrasion, the natural oxide layer and the non-oxide layer have different melting properties. Variations of the depth of focus of the laser beam greatly affect variations of the height of produced fine surface irregularities, making it difficult to form fine surface irregularities that are of a uniform height.
Efforts have been made to form the texture with an energy ion beam. According to this process, an ion beam or plasma is used to produce a fine surface irregularity structure, and generated ions are electrically accelerated and applied to the disk surface for thereby processing the disk surface. A resist film pattern according to the photolithography technology is used to pattern the disk surface to form the fine surface irregularity structure. Since, however, the resist film pattern is generally of an insulating material, it suffers the problem of being charged up.
As described above, a natural oxide layer is formed on the outermost layer of a metal surface. Because the natural oxide layer is highly insulative, it tends to be charged up in the process which uses an ion beam or plasma, causing changes in the path of energy ions and fluctuations of the characteristics of the applied energy. As a consequence, the surface roughness is impaired, and the amount of local processing is not made uniform.
There are also processes of forming a surface irregularity structure on the surface of a glass substrate by dissolving the surface with a vapor of hydrofluoric acid or a method of crystalline deposition. These processes are also disadvantageous in that the accuracy is poor and the surface irregularities suffer large variations, which also make it difficult to use a semicontact head.
Specifically, because the process to dissolve the surface with a vapor of hydrofluoric acid uses variations of the amount of the vapor adsorbed to the glass substrate, the vapor density nonuniformities cause variations of the depth to which the surface is dissolved, increasing processed surface depth nonuniformities. Consequently, it is impossible to form fine surface irregularities having a height of 20 xcexcm, for example, over the entire surface of the glass substrate with a uniform processed surface depth and a uniform density. The process based on crystalline deposition controls the crystal form of the glass through heat treatment for controlling the size and quantity of crystal particles separated on the surface according to the temperature. It is difficult to form fine surface irregularities over the surface of the glass substrate with a uniform processed surface depth and a uniform density because of nonuniform heat treatment, nonuniform crystal grain size, and nonuniform separated particles.
The present invention has been made in view of the above drawbacks. It is an object of the present invention to provide a magnetic recording disk having on its surface a texture structure of fine surface irregularities with reduced variations which is suitable for high-density magnetic recording, and a method of manufacturing such a magnetic recording disk.
According to the present invention, there is provided a magnetic recording disk having a substrate coated on a surface thereof with a magnetic layer, a carbon layer, and a lubricating film. The substrate has on a surface thereof a texture structure of fine surface irregularities for reducing friction when the substrate is brought into contact with a head and for controlling an amount of lift of the head. The fine surface irregularities have a height of 20 nm or less and are formed from a pattern shape or profile of a shield with a high-speed atomic beam emitted from a high-speed atomic beam source.
With the above arrangement of the invention, the magnetic recording disk has surface irregularities formed uniformly on its entire surface, the surface irregularities having a height of 20 nm or less. The amount of a lift of a head from the disk is reduced, and the head is not attracted to the disk. Therefore, the disk has a greatly increased magnetic recording density.
The substrate can be made of an aluminum material coated on a surface thereof with an Nixe2x80x94P layer, with the surface irregularities being formed on said Nixe2x80x94P layer.
The substrate can be made of an aluminum material coated on a surface thereof with an Nixe2x80x94P layer, with the surface irregularities being formed on the surface of the aluminum material.
The substrate can be made of an aluminum material coated on a surface thereof with a carbon layer, with the surface irregularities being formed on said carbon layer.
The substrate comprises a glass substrate, and the surface irregularities can be formed on a surface of said glass substrate.
The substrate comprises a glass substrate, and the surface irregularities can be formed on said carbon layer.
According to the present invention, there is also provided a method of producing a magnetic recording disk having a substrate coated on a surface with successive films including a magnetic layer, a carbon layer, and a lubricating film. The method includes forming a texture structure of fine surface irregularities on a surface of said substrate or any one of the films from a pattern shape or profile of a shield with a high-speed atomic beam.
With the above arrangement of the invention, the method is capable of forming surface irregularities having a height of 20 nm or less uniformly on the entire surface of the magnetic recording disk within a short period of time. The amount of a lift of a head from the disk is reduced, and the head is not attracted to the disk. Therefore, the disk has a greatly increased magnetic recording density.
The high-speed atomic beam may be emitted from a high-speed atomic beam source using an inert gas such as an argon gas.
The high-speed atomic beam may also be emitted from a high-speed atomic beam source using a chlorine gas or a chlorine-based compound gas.
In order to form the fine surface irregularities on the surface of said substrate or any one of the films, fine particles are dispersed and placed on the surface of the substrate or any one of the films. Thereafter the high-speed atomic beam is applied to the surface to form the fine surface irregularities with a profile of the fine particles. The shield can thus easily be scattered and placed without relying on complex photolithography or the like.
The high-speed atomic beam may be emitted from a parallel-plate-type high-speed atomic beam source.
According to the present invention, there is further provided a method of producing a magnetic recording disk having a substrate coated on a surface with successive films including a magnetic layer, a carbon layer, and a lubricating film. This method includes applying a solution with substantially spherical fine particles dispersed therein to the surface of the substrate or a surface of any one of the films to scatter and place said fine particles on said surface, then applying a high-speed atomic beam from a parallel-plate-type high-speed atomic beam source to said surface to form surface irregularities on said surface with said fine particles serving as a shield, and then removing said fine particles from said surface by cleaning the surface.
The fine particles may comprise fine crystalline particles of any one of alumina, carbon, Si3N4, SiC, TiN, ZrO2, and MgO.